How do I weight paint belts and straps?
I had similar problem for shoulders straps. Three points here in my experience :


Weight the buckle the same weights (uniformally)
Weight the extremities of the straps the same as the buckle
Space the next straps vertices at the first point of the cat shape they need to be "linked" to


Something like that https://gyazo.com/87bf0a45e2723b477d715645ae540be6
The idea is to keep the buckle linked to somekind of tangent point of the cat belly. And for the strap, to allow them to stretch between the buckle and the next "on skin" vertices.

Another way to obtain the result (maybe) is to shape all straps starting from the cat curves (using the knife tool probably : copy the cat and cut) so that you both keep the appropriate weights (from the cat) and also give all the good bending edges inside of the model. That can probably be easily done for the straps... but more difficult for the buckle.